1. Field of the Invention
The present disclosure relates generally to track guiding systems for guiding travel of an object along a defined path, and more particularly to a track guiding system for guiding travel of an object along a vertical path.
2. Description of the Related Art
A top drive is an example of a device requiring guided travel along a defined path. In this case, the defined path is a vertical path. The top drive is used to rotate a drill string from the top of the drill string, typically while the drill string is in a borehole. The top drive includes at least one motor and a gear system. The motor is coupled to the gear system, and the gear system is connected to a short pipe, which is in turn attached to the top of the drill string. The top drive is suspended on a hook at the end of a traveling block. The traveling block itself is suspended by cables from the top of a derrick. The traveling block moves up and down the derrick by means of the cables, and the top drive moves with the traveling block. A track guiding system is used to guide the travel of the top drive in a vertical direction along the derrick. Typically, the track guiding system includes a wheeled carriage adapted to run on a pair of vertical tracks. The vertical tracks are anchored to the rig floor or bottom of the derrick and extend up the derrick. The top drive is coupled to the wheeled carriage for guided travel up and down the vertical tracks.
FIG. 1 is a perspective view of a prior-art track guiding system for guiding travel of a top drive along a vertical path. The vertical track guiding system includes a beam 1 having parallel sides 3, 5. Tracks 4, 6 are formed at the parallel sides 3, 5, respectively. The following discussion applies to both tracks 4, 6, but only track 4 will be specifically mentioned. Track 4 consists of plates 7, 9, which are welded to the side 3 of the beam 1. The plates 7, 9 are spaced apart to define a channel 15. Rollers 17, which are coupled to a carriage 21, travel in and along the channel 15. The rollers 17 and carriage 21 constitute a wheeled carriage. In use, the top drive (not shown) would be mounted on the carriage 21 for guided travel along the tracks 4, 6.
For the vertical track guiding system of FIG. 1, ideally, the plates 7, 9 should be parallel so that the channel 15 has a constant width along the length of the beam 1, the width being the gap between the plates 7, 9. However, because of distortion of the plates 7, 9, either during manufacturing of the plates or attachment of the plates to the beam 1, the plates 7, 9 will not be truly parallel. Non-parallelism would occur even if the plates 7, 9 were initially precisely positioned on the beam 1. Very often, the width at one or more points in the channel 15 will be smaller than the width of the rollers 17 so that the rollers 17 become periodically jammed in the channel 15. A pulling force applied to the top drive (not shown) coupled to the carriage 21 will dislodge the rollers 17 from the jammed position, but at a cost, i.e., the rollers 17 will deform the plates 7, 9. At these deformed locations in the channel 15, the rollers 17 will either wobble or slide (as opposed to roll) along the plates 7,9.
Typically, several lengths of beams are stringed together to form a sufficient length of track to guide the travel of the top drive up and down the derrick. Connections between the plates on adjacent beams are typically not smooth, particularly because it is difficult to make two beams and plate attachments that have the same dimensions and tolerances. Rollers tend to jump when they encounter these non-smooth connections.
Wobbling, sliding or jumping of the rollers will adversely affect the stability of the top drive as the top drive travels up and down the guiding system. Instability of the top drive may, in turn, affect the quality of the borehole being drilled by the drill string. Deformation of the track plates may also reduce longevity of the track guiding system.
While the top drive is coupled to a guided wheeled carriage and used to rotate a drill string, the axial axis of the top drive needs to be aligned with the vertical. In the current art, a screw-type fixed-adjustment mechanism is used initially to adjust the verticality of the top drive. Subsequent adjustments may take place at regular operating time intervals or when required. In the current art, operators have to periodically, or as required, physically measure the verticality of tracks at a given position along the tracks where the top drive is located and then adjust the verticality of the top drive based on this measurement. With this approach, verticality is adjusted for a given position of the top drive along the tracks. Since it is unknown how the tracks will deform while in operation or after a certain period, the verticality adjustment of the top drive is valid only for the given position of the top drive along the tracks. During drilling, the position of the top drive along the tracks will vary, and the top drive may not be truly vertical for a portion of its travel along the tracks. This can result in drilling of a poor-quality borehole, e.g., one having a non-uniform cross-section where a uniform cross-section is desired.
The present disclosure is directed to various methods and devices that may avoid, or at least reduce, the effects of one or more of the problems identified above.